Hydrogen is an attractive fuel because it is clean and can be used to efficiently produce electricity in a fuel cell. The automotive industry expends significant resources in the development of hydrogen fuel cells as a source of power for vehicles. Such vehicles would be more efficient and generate fewer emissions than today's vehicles employing internal combustion engines.
A hydrogen fuel cell is an electrochemical device that may include an anode and a cathode with an electrolyte therebetween. The anode receives hydrogen gas and the cathode receives oxygen or air. The hydrogen gas is dissociated in the anode to generate free protons and electrons. The protons pass through the electrolyte to the cathode. The protons react with the oxygen and the electrons in the cathode to generate water. The electrons from the anode cannot pass through the electrolyte, and thus are directed through an electrical load to perform work before being sent to the cathode. The work can act in various ways to operate the vehicle.
Proton exchange membrane (PEM) fuel cells are one type of fuel cells that may be used in vehicles. A PEM fuel cell generally includes a solid polymer electrolyte proton-conducting membrane, such as a perfluorosulfonic acid membrane. The anode and cathode typically include finely divided catalytic particles, usually platinum, supported on carbon particles and mixed with an ionomer. The catalytic mixture is deposited on opposing sides of the membrane. The combination of the anode catalytic mixture, the cathode catalytic mixture and the membrane define a membrane electrode assembly (MEA). MEAs are relatively expensive to manufacture and require certain conditions for effective operation. These conditions include proper water management and humidification and control of catalyst poisoning constituents, such as carbon monoxide.
Several fuel cells are typically combined into a fuel cell stack to generate the desired power. The fuel cell stack receives an anode input gas, typically a fuel such as hydrogen, that flows into the anode side of the stack. The fuel cell also receives a cathode input gas, typically a flow of compressed air. Not all of the oxygen in the cathode gas is consumed by the stack and some of the air is output as a cathode exhaust gas that may include water as a stack by-product.
The fuel cell stack may include a series of flow field plates or bipolar plate assemblies positioned between the several MEAs in the stack. The bipolar plates include an anode side and a cathode side for adjacent fuel cells in the stack. Anode gas flow channels may be provided in the anode side of the bipolar plates that allow the anode gas to flow to the anode side of each MEA. Cathode gas flow channels may be provided in the cathode side of the bipolar plates that allow the cathode gas to flow to the cathode side of each MEA. The bipolar plates are generally made of and/or have surfaces made of a conductive material, such as stainless steel or other conductive material, so that they conduct the electricity generated by the fuel cells from one cell to the next cell as well as out of the stack.
The fuel cells of the fuel cell stack may receive and release reactant gases and/or other fuel cell fluids via various reactant headers. A reactant header may run alongside or within the length of the fuel cell stack to distribute or receive reactant gases to or from each individual fuel cell in a parallel arrangement.
Various configurations have been developed to transport fuel cell fluids such as gaseous fuels, reactants, and reactant by-products to and from reactant headers and fuel cell reactant flow channels.